U.S. patent application number 13/205656 was filed with the patent office on 2011-12-08 for sintered body of low temperature cofired ceramic and multilayer ceramic substrate.
This patent application is currently assigned to MURATA MANUFACTURING CO., LTD.. Invention is credited to Tsuyoshi KATSUBE.
Application Number | 20110300355 13/205656 |
Document ID | / |
Family ID | 42561812 |
Filed Date | 2011-12-08 |
United States Patent
Application |
20110300355 |
Kind Code |
A1 |
KATSUBE; Tsuyoshi |
December 8, 2011 |
SINTERED BODY OF LOW TEMPERATURE COFIRED CERAMIC AND MULTILAYER
CERAMIC SUBSTRATE
Abstract
In a sintered body of low temperature cofired ceramic
constituting ceramic layers of a multilayer ceramic substrate
provided with external conductor films, which is obtained by
sintering a non-glass low temperature cofired ceramic material,
respective crystalline phases of quartz, alumina, and fresnoite are
deposited. The ceramic layers are, because of being in the form of
a sintered body of non-glass low temperature cofired ceramic, less
likely to fluctuate in composition, and the multilayer ceramic
substrate can be thus inexpensively and easily manufactured
therefrom. In addition, the ceramic layers have the above-mentioned
respective crystalline phases deposited therein, and thus have a
high joint strength with the external conductor films, and
moreover, the sintered body itself has a high fracture toughness
value.
Inventors: |
KATSUBE; Tsuyoshi;
(Nagaokakyo-shi, JP) |
Assignee: |
MURATA MANUFACTURING CO.,
LTD.
Nagaokakyo-shi
JP
|
Family ID: |
42561812 |
Appl. No.: |
13/205656 |
Filed: |
August 9, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
PCT/JP2010/051929 |
Feb 10, 2010 |
|
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13205656 |
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Current U.S.
Class: |
428/210 ;
501/135 |
Current CPC
Class: |
C04B 2235/3232 20130101;
C04B 2235/3284 20130101; C04B 2235/786 20130101; C04B 35/14
20130101; C04B 35/62645 20130101; C04B 2235/3262 20130101; C04B
2235/9669 20130101; C04B 2235/96 20130101; C04B 35/638 20130101;
C04B 2235/6025 20130101; C04B 35/62685 20130101; C04B 2235/3215
20130101; C04B 2235/3217 20130101; C04B 2235/3275 20130101; C04B
2235/3244 20130101; C04B 2235/3251 20130101; C04B 2237/341
20130101; C04B 2235/72 20130101; C04B 2235/3229 20130101; H05K
1/0306 20130101; H05K 3/4629 20130101; Y10T 428/24926 20150115;
B32B 18/00 20130101; C04B 2235/3206 20130101; C04B 2235/6584
20130101; C04B 2235/3239 20130101; C04B 35/195 20130101; C04B
2235/442 20130101; C04B 2235/3272 20130101; C04B 2235/3418
20130101 |
Class at
Publication: |
428/210 ;
501/135 |
International
Class: |
B32B 18/00 20060101
B32B018/00; C04B 35/10 20060101 C04B035/10; C04B 35/01 20060101
C04B035/01 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 16, 2009 |
JP |
2009-032650 |
Claims
1. A sintered body of low temperature cofired ceramic obtained by
sintering a non-glass low temperature cofired ceramic material,
wherein respective crystalline phases of quartz, alumina, and
fresnoite are deposited in the sintered body.
2. The sintered body of low temperature cofired ceramic according
to claim 1, wherein at least one crystalline phase of sanbornite
and celsian is further deposited in the sintered body.
3. The sintered body of low temperature cofired ceramic according
to claim 1, wherein the fresnoite crystalline phase is included in
a ratio of about 1 weight % to about 20 weight %.
4. The sintered body of low temperature cofired ceramic according
to claim 1, wherein the fresnoite crystalline phase has an average
crystal grain size of about 5 .mu.m or less.
5. The sintered body of low temperature cofired ceramic according
to claim 1, wherein the non-glass low temperature cofired ceramic
material includes a main constituent ceramic material containing a
Si oxide, a Ba oxide, and an Al oxide, and an accessory constituent
ceramic material containing a Mn oxide and a Ti oxide, and contains
substantially neither of a Cr oxide and a B oxide.
6. A multilayer ceramic substrate comprising: a laminate including
a plurality of ceramic layers stacked on each other; and conductor
patterns containing gold, silver, or copper as a main constituent,
the conductor patterns provided on a surface layer of and an inner
layer of the laminate; wherein the ceramic layers are obtained by
sintering a non-glass low temperature cofired ceramic material and
are constituted by a sintered body of low temperature cofired
ceramic in which respective crystalline phases of quartz, alumina,
and fresnoite are deposited.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a sintered body of low
temperature cofired ceramic obtained by firing a non-glass low
temperature cofired ceramic material, and to a multilayer ceramic
substrate including the sintered body of low temperature cofired
ceramic.
[0003] 2. Description of the Related Art
[0004] A sintered body of low temperature cofired ceramic (LTCC:
Low Temperature Cofired Ceramic) is obtained by forming a low
temperature cofired ceramic material into a predetermined shape and
subjecting this material having the predetermined shape to
sintering.
[0005] The low temperature cofired ceramic material can be
subjected to cofiring with a low melting point metal material such
as silver or copper with a relatively small specific resistance,
thus, can form multilayer ceramic substrates which are excellent in
terms of high frequency characteristics, and has been used as, for
example, a substrate material for high frequency modules in
information-communication terminals.
[0006] While a ceramic material such as Al.sub.2O.sub.3 mixed with
a B.sub.2O.sub.3--SiO.sub.2 based glass material, a so-called
glass-ceramic composite system is typically used as the low
temperature cofired ceramic material, this system requires the use
of a relatively expensive glass material as a starting raw
material, and in addition, contains boron which is likely to
volatilize during firing. Therefore, substrates obtained are likely
to fluctuate in composition, and thus, the manufacturing process of
the substrates is complicated, such as having to use a special
setter for controlling the volatilization amount of boron.
[0007] Accordingly, low temperature cofired ceramic materials have
been proposed as described in, for example, Japanese Patent
Application Laid-Open No. 2002-173362, Japanese Patent Application
Laid-Open No. 2008-044829, and Japanese Patent Application
Laid-Open No. 2008-053525. The low temperature cofired ceramic
materials described in these documents will not encounter the
problem as described, because the starting raw materials contain no
glass, and moreover, because the low temperature cofired ceramic
materials are non-glass low temperature cofired ceramic materials
containing no boron.
[0008] However, sintered bodies of low temperature cofired ceramic
obtained by sintering the low temperature cofired ceramic materials
described in these documents may have an insufficient joint
strength with a conductor film formed on the surface thereof in
some case, and in addition, the sintered bodies themselves have a
small fracture toughness value, and thus, may fail to provide
desired strength properties in some cases.
SUMMARY OF THE INVENTION
[0009] In view of the actual circumstances described above,
preferred embodiments of the present invention provide a sintered
body of non-glass low temperature cofired ceramic which can be
manufactured inexpensively and easily without using glass for a
staring raw material, has a high joint strength with a conductor
film, and has a high fracture toughness value.
[0010] In addition, preferred embodiments of the present invention
provide a multilayer ceramic substrate with high reliability, which
includes a plurality of ceramic layers made of the sintered body of
low temperature cofired ceramic.
[0011] A sintered body of low temperature cofired ceramic according
to a preferred embodiment of the present invention is obtained by
sintering a non-glass low temperature cofired ceramic material, and
includes respective crystalline phases of quartz, alumina, and
fresnoite deposited therein.
[0012] Another preferred embodiment of the present invention
provides a multilayer ceramic substrate including a laminate
including a plurality of ceramic layers stacked on each other; and
conductor patterns containing gold, silver, or copper as their main
constituent, the conductor patterns provided on a surface layer of
and an inner layer of the laminate. In the multilayer ceramic
substrate according to a preferred embodiment of the present
invention, the ceramic layers are preferably obtained by sintering
a non-glass low temperature cofired ceramic material and are
constituted by a sintered body of low temperature cofired ceramic
in which respective crystalline phases of quartz, alumina, and
fresnoite are deposited.
[0013] The sintered body of low temperature cofired ceramic
according to a preferred embodiment of the present invention is
obtained by sintering a non-glass low temperature cofired ceramic
material, and thus, is less likely to fluctuate in composition and
is inexpensive, and in addition, the manufacturing process of the
sintered body is easy because the sintered body can be fired
without the use of any special setter. Furthermore, the sintered
body has the respective crystalline phases of quartz, alumina, and
fresnoite deposited, and thus has a high joint strength with a
conductor film formed on the surface thereof, and moreover, the
sintered body itself has a high fracture toughness value, and thus
has excellent strength properties.
[0014] Likewise, the multilayer ceramic substrate according to a
preferred embodiment of the present invention is less likely to
fluctuate in composition and is inexpensive because the ceramic
layers constituting the multilayer ceramic substrate are obtained
by sintering a non-glass low temperature cofired ceramic material,
and in addition, can be manufactured easily because the multilayer
ceramic substrate can be fired without the use of any special
setter. Furthermore, the ceramic layers have the respective
crystalline phases of quartz, alumina, and fresnoite deposited, and
thus have a high joint strength with an external conductor film
formed on the surface thereof, and moreover, the sintered body
itself has a high fracture toughness value, and thus allows the
multilayer ceramic substrate including the ceramic layers to have
excellent strength properties with high reliability.
[0015] The above and other elements, features, steps,
characteristics and advantages of the present invention will become
more apparent from the following detailed description of the
preferred embodiments with reference to the attached drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] The FIGURE is a cross-sectional view schematically
illustrating a multilayer ceramic substrate 1 configured with the
use of a sintered body of low temperature cofired ceramic according
to a preferred embodiment of the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0017] The sintered body of low temperature cofired ceramic
according to a preferred embodiment of the present invention is
obtained by sintering a non-glass low temperature cofired ceramic
material, in which respective crystalline phases of quartz
(SiO.sub.2), alumina (Al.sub.2O.sub.3), and fresnoite
(Ba.sub.2TiSi.sub.2O.sub.8) are deposited. In this case, the
"sintered body of low temperature cofired ceramic" refers to a low
temperature cofired ceramic material subjected to sintering at a
firing temperature of, for example, 1050.degree. C. or less, which
can be cofired with a low melting point metal material such as
gold, silver, or copper with a small specific resistance.
Furthermore, while the starting raw material contains substantially
no glass constituent, the sintered body itself includes an
amorphous section in addition to the respective crystalline phases
described above. This is because when the non-glass low temperature
cofired ceramic material is subjected to firing, the starting raw
material thereof is partially turned into glass.
[0018] The sintered body of low temperature cofired ceramic
according to a preferred embodiment of the present invention has
the crystalline phases described above as main crystalline phases,
and thus has a small specific dielectric constant .di-elect
cons..sub.r of 10 or less, allowing for the achievement of a
sintered body of low temperature cofired ceramic which is suitable
for ceramic layers constituting substrates for high frequencies.
Moreover, the sintered body of low temperature cofired ceramic has
a high joint strength with the external conductor film as described
above, and thus has an improved electrode peel strength, thereby
making problems less likely to be caused such as loss of on-board
surface mounted components. Furthermore, the sintered body of low
temperature cofired ceramic can form ceramic layers with a high
fracture toughness value, thus allowing for the achievement of a
multilayer ceramic substrate with excellent reliability.
[0019] In the sintered body of low temperature cofired ceramic
according to a preferred embodiment of the present invention, at
least one crystalline phase of sanbornite (BaSi.sub.2O.sub.5) and
celsian (BaAl.sub.2Si.sub.2O.sub.8) is further deposited
preferably. This deposition of the crystalline phases of sanbornite
and celsian results in the presence of various types of crystalline
phases in large numbers, and as a result, the resultant
heterogeneous crystal structure of the sintered body can, even when
the sintered body is cracked, suppress the development of the
crack. It is more preferable that the respective crystalline phases
of sanbornite and celsian be both deposited.
[0020] In the sintered body of low temperature cofired ceramic
according to a preferred embodiment of the present invention, the
fresnoite crystalline phase is preferably included in a ratio of
about 1 weight % to about 20 weight %, for example. This
appropriate deposition amount of the fresnoite crystalline phase
prevents the segregation of the crystalline phase to further
improve the joint strength of the external conductor film, and thus
further increase the electrode peel strength.
[0021] In addition, in the sintered body of low temperature cofired
ceramic according to a preferred embodiment of the present
invention, the fresnoite crystalline phase preferably has an
average crystal grain size of about 5 .mu.m or less, for example.
More specifically, the presence of this fine crystalline phase in a
predetermined ratio can increase crystal grain boundaries to
suppress, even when the sintered body is cracked, the development
of the crack.
[0022] In addition, the non-glass low temperature cofired ceramic
material constituting the sintered body of low temperature cofired
ceramic according to a preferred embodiment of the present
invention preferably includes a main constituent ceramic material
containing a Si oxide, a Ba oxide, and an Al oxide, and an
accessory constituent ceramic material containing a Mn oxide and a
Ti oxide, and contains substantially neither of a Cr oxide and a B
oxide. The term "substantially" in this case means that a Cr oxide
and a B oxide can be contained as impurities at less than about 0.1
weight %, for example. More specifically, even when a Cr oxide and
a B oxide are mixed as impurities, the effects of a preferred
embodiment of the present invention can be achieved as long as the
Cr oxide and the B oxide are less than about 0.1 weight %.
[0023] More particularly, this low temperature cofired ceramic
material preferably includes a main constituent ceramic material
containing about 48 weight % to about 75 weight % of Si in terms of
SiO.sub.2, about 20 weight % to about 40 weight % of Ba in terms of
BaO, and about 5 weight % to about 20 weight % of Al in terms of
Al.sub.2O.sub.3, and an accessory constituent ceramic material
containing about 2 parts to about 10 parts by weight of Mn in terms
of MnO and about 0.1 parts to about 10 parts by weight of Ti in
terms of TiO.sub.2 with respect to 100 parts by weight of the main
constituent ceramic material, and contains substantially neither of
a Cr oxide and a B oxide.
[0024] This low temperature cofired ceramic material is a non-glass
low temperature cofired ceramic material containing no boron
because no glass is used as a starting raw material, and thus, a
sintered body obtained is less likely to fluctuate in composition,
and the firing process therefor can be managed easily. Moreover,
the sintered body obtained itself has a high strength with a
bending strength of about 230 MPa or more, and in the case of using
this sintered body as a substrate, the substrate provides high
reliability with a high peel strength and thus a high joint
strength with the external conductor film. In addition, the
promoted crystallization can improve the resistance to environments
such as high temperatures and high humidity, and even improve the
chemical resistance of the substrate such as an ability to prevent
the elution of the substrate constituent into a plating solution.
Furthermore, the promoted crystallization thus provides a
multilayer ceramic substrate including a small amorphous section
with a high Qf value.
[0025] In this case, the main constituent ceramic material
containing about 48 weight % to about 75 weight % of Si in terms of
SiO.sub.2, about 20 weight % to about 40 weight % of Ba in terms of
BaO, and about 5 weight % to about 20 weight % of Al in terms of
Al.sub.2O.sub.3 is a basis constituent of the sintered body
obtained, which makes a significant contribution to the achievement
of a sintered body with a high insulation resistance, a small
specific dielectric constant .di-elect cons..sub.r, and a small
dielectric loss.
[0026] On the other hand, Mn (particularly MnO) as the accessory
constituent ceramic material is likely to react with the
SiO.sub.2--BaO--Al.sub.2O.sub.3 based main constituent ceramic
material to create a liquid phase constituent, and acts as a
sintering aid by reducing the viscosity of the starting raw
material during firing, but has much lower volatility as compared
with B.sub.2O.sub.3 which likewise acts as a sintering aid.
Therefore, Mn reduces fluctuation in firing, makes it easy to
manage the firing process, and makes a contribution to an
improvement in productivity.
[0027] In addition, Ti (particularly TiO.sub.2) as the accessory
constituent ceramic material can increase, although the detailed
mechanism is not known, the reactivity between the ceramic layers
made of the low temperature cofired ceramic material and the
external conductor film made of a low melting point metal material
such as copper, and the cofiring process can increase the joint
strength between the sintered body and the conductor film, that is,
the joint strength between the ceramic layers and the external
conductor film. As a result, strong soldered joints are formed
between active elements such as a semiconductor device and passive
elements such as a chip capacitor, which are mounted on the
multilayer ceramic substrate, and the multilayer ceramic substrate,
thereby allowing the joints to be prevented from breaking due to
shock such as fall of the element.
[0028] It is to be noted that this low temperature cofired ceramic
material may further contain, in place of Ti mentioned above, or in
addition to Ti, Fe (particularly Fe.sub.2O.sub.3) as an accessory
constituent ceramic material. In this case, the content of Fe is
preferably about 0.1 parts to about 10 parts by weight in total in
conjunction with the Ti oxide with respect to 100 parts by weight
of the main constituent ceramic material. This Fe can also increase
the reactivity between the ceramic layers and the external
conductor film, and the cofiring process can increase the joint
strength between the sintered body and the conductor film, that is,
the joint strength between the ceramic layers and the external
conductor film.
[0029] In addition, this low temperature cofired ceramic material
containing substantially no B oxide (particularly B.sub.2O.sub.3)
can thus reduce the fluctuation in composition during firing of the
material, and make it easy to manage the firing process, such as
the elimination of the need for a special setter. In addition, the
low temperature cofired ceramic material containing substantially
no Cr oxide (particularly Cr.sub.2O.sub.3) can thus prevent the
decrease in Qf value in a high-frequency band typified by a
microwave band, and for example, a Qf value of 1000 or more can be
achieved at 3 GHz.
[0030] This low temperature cofired ceramic material preferably
contains no alkali metal oxide such as Li.sub.2O or Na.sub.2O. This
is because these alkali metal oxides are also likely to be volatile
during firing as in the case of B.sub.2O.sub.3, which may cause
fluctuation in the composition of a substrate obtained.
[0031] Furthermore, when the low temperature cofired ceramic
material contains none of these alkali metal oxides, the resistance
to environments such as high temperatures and high humidity can be
improved, and the chemical resistance such as an ability to prevent
the elution into a plating solution can be even improved.
[0032] This low temperature cofired ceramic material preferably
further contains, as an accessory constituent ceramic material,
about 0.1 parts to about 5 parts by weight of Mg in terms of MgO
with respect to 100 parts by weight of the main constituent ceramic
material. This Mg (particularly MgO) contained in the low
temperature cofired ceramic material promotes the crystallization
of the low temperature cofired ceramic material during firing,
thereby allowing for the reduction in the volume of a liquid phase
section which causes a decrease in substrate strength, and allowing
for a further improvement in the bending strength of a sintered
body obtained.
[0033] In addition, this low temperature cofired ceramic material
preferably further contains, as an accessory constituent ceramic
material, about 0.1 parts to about 6 parts by weight of at least
one selected from among Nb, Ce, Zr, and Zn respectively in terms of
Nb.sub.2O.sub.5, CeO.sub.2, ZrO.sub.2, and ZnO with respect to 100
parts by weight of the main constituent ceramic material. The at
least one selected from among Nb, Ce, Zr, and Zn (particularly at
least one oxide selected from among Nb.sub.2O.sub.5, CeO.sub.2,
ZrO.sub.2, and ZnO) contained in the low temperature cofired
ceramic material can reduce the additive amount of Mn (particularly
MnO) which is likely to remain as an amorphous constituent, thereby
allowing for the reduction in the volume of a liquid phase section
which causes a decrease in substrate strength, and allowing for a
further improvement in the bending strength of a multilayer ceramic
substrate obtained.
[0034] In addition, this low temperature cofired ceramic material
may further contain, as an accessory constituent ceramic material,
about 0.1 parts to about 5.0 parts by weight of Co and/or V
respectively in terms of CoO and V.sub.2O.sub.5 with respect to 100
parts by weight of the main constituent ceramic material. These
constituents can improve the bending strength of a multilayer
ceramic substrate obtained, and also functions as a coloring
agent.
[0035] The sintered body of low temperature cofired ceramic
according to a preferred embodiment of the present invention can be
manufactured by adding and mixing a ceramic powder of MnCO.sub.3 as
well as at least one ceramic powder of TiO.sub.2 and
Fe.sub.2O.sub.3 to and with respective ceramic powders of
SiO.sub.2, BaCO.sub.3, and Al.sub.2O.sub.3 to obtain a low
temperature cofired ceramic material, forming the low temperature
cofired ceramic material into a predetermined shape, and further
subjecting this compact to firing. Preferably, the sintered body of
low temperature cofired ceramic is manufactured through a step of
adding at least one ceramic powder of TiO.sub.2 and Fe.sub.2O.sub.3
to respective ceramic powders of SiO.sub.2, BaCO.sub.3, and
Al.sub.2O.sub.3 to obtain a mixture and subjecting the mixture to
calcination, thereby preparing a calcined powder, and a step of
adding, to the calcined powder, a ceramic powder of MnCO.sub.3
subjected to no calcination.
[0036] Therefore, a ceramic green sheet including the low
temperature cofired ceramic material described above is preferably
manufactured through a step of adding at least one ceramic powder
of TiO.sub.2 and Fe.sub.2O.sub.3 to respective ceramic powders of
SiO.sub.2, BaCO.sub.3, and Al.sub.2O.sub.3 to obtain a mixture and
subjecting the mixture to calcination, thereby preparing a calcined
powder, a step of adding, to the calcined powder, a ceramic powder
of MnCO.sub.3 subjected to no calcination, and a binder, thereby
preparing a ceramic slurry, and a step of forming the ceramic
slurry into a shape, thereby forming a ceramic green sheet.
[0037] As described above, for the manufacture of the low
temperature cofired ceramic material or the ceramic green sheet, as
long as a Mn constituent subjected to no calcination is added to a
calcined powder obtained by calcination of a Si constituent, a Ba
constituent, an Al constituent, and Ti/Fe constituent, the reaction
of calcination synthesis is suppressed during the calcination, and
the grain size for the calcined powder can be thus made smaller.
Therefore, the step of grinding the calcined powder can be
simplified, and the reduction in layer thickness can be easily
advanced for ceramic green sheets prepared with the use of the
calcined powder. In addition, the calcined powder can be prevented
from undergoing a color change into a dark brown, and thus, in
particular, in the case of printing a conductive paste containing
copper as its main constituent, ceramic green sheets prepared with
the use of this type of calcined powder can be improved in terms of
image recognition.
[0038] Next, a multilayer ceramic substrate configured with the use
of the sintered body of low temperature cofired ceramic according
to a preferred embodiment of the present invention, and a method
for manufacturing the multilayer ceramic substrate will be
described with reference to a preferred embodiment shown in the
FIGURE.
[0039] The FIGURE is a cross-sectional view schematically
illustrating a multilayer ceramic substrate 1 including a sintered
body of low temperature cofired ceramic according to a preferred
embodiment of the present invention.
[0040] The multilayer ceramic substrate 1 includes a laminate 3
including a plurality of stacked ceramic layers 2. The ceramic
layers 2 included in the laminate 3 are constituted by the sintered
body of low temperature cofired ceramic according to a preferred
embodiment of the present invention. In this laminate 3, various
types of conductor patterns are provided in connection with
specific ones of the ceramic layers 2.
[0041] The conductor patterns described above include several
external conductor films 4 and 5 located on end surfaces in the
stacking direction of the laminate 3, several internal conductor
films 6 arranged along the specific interfaces between the ceramic
layers 2, and via hole conductors 7 formed through specific ones of
the ceramic layers 2, which function as interlayer connecting
conductors.
[0042] The external conductor films 4 provided on the surface of
the laminate 3 are used for connections to electronic components 8
and 9 to be mounted on the outer surface of the laminate 3. The
FIGURE illustrates the electronic component 8 including bump
electrodes 10, for example, like a semiconductor device, and the
electronic component 9 including flat terminal electrodes 11, for
example, like a chip capacitor. In addition, the external conductor
films 5 located on the lower surface of the laminate 3 are used for
connection to a mother board (not shown) on which this multilayer
ceramic substrate 1 is to be mounted.
[0043] The laminate 3 included in this type of multilayer ceramic
substrate 1 is obtained by firing a raw laminate including a
plurality of stacked ceramic green layers to serve as the ceramic
layers 2, and the internal conductor films 6 and via hole
conductors 7 including a conductive paste, and in some cases,
further including the external conductor films 4 and 5 including a
conductive paste.
[0044] The stacked structure of the ceramic green layers in the raw
laminate described above is provided typically by stacking multiple
ceramic green sheets obtained by shape forming of a ceramic slurry,
and the conductor patterns, in particular, the internal conductor
patterns are provided on the ceramic green sheets before the
stacking.
[0045] The ceramic slurry can be obtained by adding, to the low
temperature cofired ceramic material described above, an organic
binder such as polyvinyl butyral, a solvent such as toluene and
isopropyl alcohol, a plasticizer such as di-n-butylphthalate, and
in addition, if necessary, additives such as a dispersant for the
formation of a slurry.
[0046] In the shape forming for obtaining the ceramic green sheets
with the use of the ceramic slurry, for example, a doctor blade
method is applied on a carrier film made of an organic resin such
as polyethylene terephthalate to form the ceramic slurry into a
sheet shape.
[0047] For providing the conductor patterns on the ceramic green
sheets, with the use of a conductive paste containing, as a main
constituent of its conductive constituent, a low melting point
metal material such as gold, silver, or copper, through holes for
the via hole conductors 7 are provided in the ceramic green sheets,
and filled with the conductive paste, and conductive paste films
for the internal conductor films 6 and conductive paste films for
the external conductor films 4 and 5 are formed by, for example, a
screen printing method. It is to be noted that the sintered body of
low temperature cofired ceramic according to a preferred embodiment
of the present invention is excellent in terms of cosinterability
with a conductive paste containing, in particular, copper as its
main constituent, among the low melting point metal materials of
gold, silver, or copper.
[0048] These ceramic green sheets are stacked in a predetermined
order, and subjected to pressure bonding with a pressure, for
example, about 1000 kgf/cm.sup.2 to about 1500 kgf/cm.sup.2 in the
stacking direction to provide a raw laminate. This raw laminate may
be provided with, not shown, a cavity for housing other electronic
components, and with a connection to fix thereto a cover covering
the electronic components 8 and 9, etc.
[0049] The raw laminate is subjected to firing in a temperature
range not less than the temperature at which the ceramic material
contained in the ceramic green layers can be sintered, for example,
about 850.degree. C. or more, and not more than the melting point
of the metal contained in the conductor patterns, for example,
about 1050.degree. C. or less in the case of copper. This firing
makes the ceramic green layers sintered, and also makes the
conductive pastes sintered, thereby forming a circuit pattern with
the sintered conductor films.
[0050] Further, in particular, when the main constituent metal
contained in the conductor patterns is copper, the firing is
carried out in a non-oxidizing atmosphere such as a nitrogen
atmosphere, for example, in such a way that the removal of the
binder is completed at a temperature of about 900.degree. C. or
less, and the copper is not substantially oxidized at the
completion of the firing by decreasing the oxygen partial pressure
with decrease in temperature. Further, when the firing temperature
is, for example, about 980.degree. C. or more, it is difficult to
use silver as the metal contained in the conductor patterns.
However, it is possible to use, for example, an Ag--Pd based alloy
containing about 20 weight % or more of palladium. In this case,
the firing can be carried out in air. When the firing temperature
is, for example, about 950.degree. C. or less, silver can be used
as the metal contained in the conductor patterns.
[0051] As described above, the laminate 3 shown in the FIGURE is
obtained at the completion of the firing step.
[0052] Then, the electronic components 8 and 9 are mounted, thereby
completing the multilayer ceramic substrate 1 shown in the
FIGURE.
[0053] While the ceramic layers 2 in the multilayer ceramic
substrate 1 described above include no glass as a starting
constituent as described previously, the fired ceramic layers 2
include glass because the glass as an amorphous constituent is
produced in the firing cycle. Therefore, the multilayer ceramic
substrate 1 can be manufactured stably without the use of expensive
glass.
[0054] It is to be noted while the sintered body of low temperature
cofired ceramic according to a preferred embodiment of the present
invention is preferably applied to multilayer ceramic substrates
including a laminate which has a stacked structure as described
above, the sintered body can be also applied to ceramic substrates
which have a single layer structure simply including one ceramic
layer. In addition, the sintered body of low temperature cofired
ceramic according to a preferred embodiment of the present
invention can also be applied to composite-type multilayer ceramic
substrates including a lower dielectric constant ceramic layer made
of the sintered body of low temperature cofired ceramic and
including a higher dielectric constant ceramic layer made of
another sintered body of low temperature cofired ceramic with a
relatively high specific dielectric constant .di-elect cons..sub.r
(for example, with .di-elect cons..sub.r of 15 or more).
Experimental Example
[0055] Next, an experimental example will be described which was
carried out for confirming the effects and advantages of preferred
embodiments of the present invention.
[0056] First, respective ceramic powders of SiO.sub.2, BaCO.sub.3,
Al.sub.2O.sub.3, MnCO.sub.3, TiO.sub.2, and Mg(OH).sub.2 each with
a grain size of 2.0 .mu.m or less were prepared as starting raw
materials. Next, these starting raw material powders were weighed
so as to provide the composition ratios shown in Table 1 after
firing, subjected to wet mixing and grinding, and then to drying,
and the obtained mixtures were subjected to calcination at
750.degree. C. to 1000.degree. C. for 1 to 3 hours to obtain raw
material powders. The BaCO.sub.3 is turned into BaO after the
firing, the MnCO.sub.3 is turned into MnO after the firing, and the
Mg(OH).sub.2 is turned into MgO after the firing.
[0057] It is to be noted that in Table 1, the main constituent
ceramic material of SiO.sub.2, BaO, and Al.sub.2O.sub.3 is shown in
terms of weight % (wt %), and the SiO.sub.2, BaO, and
Al.sub.2O.sub.3 account for 100 weight % in total. On the other
hand, the accessory constituent ceramic material of MnO, TiO.sub.2,
and MgO is shown in terms of parts by weight as the ratios with
respect to 100 parts by weight of the main constituent ceramic.
TABLE-US-00001 TABLE 1 Composition of Composition of Main accessory
constituent ceramic constituent material ceramic material Sample
(wt %) (Parts by weight) No. SiO.sub.2 BaO Al.sub.2O.sub.3 MnO
TiO.sub.2 MgO 1 57.0 31.0 12.0 6.5 0.5 1.5 2 57.0 31.0 12.0 6.0 1.0
1.5 3 57.0 25.0 18.0 8.0 5.0 -- 4 63.0 22.0 15.0 10.0 10.0 -- 5
57.0 31.0 12.0 4.0 -- 2.0 6 57.0 31.0 12.0 7.0 12.0 1.0
[0058] Next, appropriate amounts of organic binder, dispersant, and
plasticizer were added to the raw material powders according to
each sample to prepare a ceramic slurry, and then, the ceramic
slurry was subjected to mixing and grinding so as to provide an
average grain size (D50) of 1.5 .mu.m or less for the raw material
powder in the slurry.
[0059] Next, the ceramic slurry was formed into a sheet shape in
accordance with a doctor blade method, subjected to drying, and cut
into an appropriate size to obtain ceramic green sheets of 50 .mu.m
in thickness.
[0060] Next, a conductive paste containing copper as its main
constituent was printed by a screen printing method onto the
predetermined ceramic green sheets to form conductor patterns to
serve as external conductor films.
[0061] Next, after the obtained ceramic green sheets were cut into
a predetermined size, the multiple ceramic green sheets were then
stacked, and then subjected to thermocompression bonding under the
conditions of temperature: 60.degree. C. to 80.degree. C. and
pressure: 1000 kg/cm.sup.2 to 1500 kg/cm.sup.2 to obtain a raw
laminate.
[0062] Next, the raw laminate was subjected to firing at a
temperature of 900.degree. C. to 1050.degree. C. in a non-oxidizing
atmosphere of nitrogen-hydrogen to obtain a plate-shaped ceramic
sintered body sample made of the cosintered ceramic green sheets
and conductor patters.
[0063] Next, the surface of the obtained sample was provided with
indentation produced by a Vickers indenter under the condition of
500 gf.times.15 seconds, and the fracture toughness value K.sub.IC
was calculated from the size of the indentation and the length of
the crack. In addition, an L-shaped lead was soldered onto a cubic
electrode of about 2 mm on a side on the surface of the obtained
sample, and the joint strength (electrode peel strength) between
the sample and the electrode was measured by a tension test in a
perpendicular direction with respect to the surface of the sample.
Furthermore, the samples were processed into a powdered form to
identify the deposited crystals from X-ray diffraction spectra, and
the ratio by weight (deposition amount) for the fresnoite
crystalline phase was calculated from the diffraction peak
intensity. In addition, the average grain size for the fresnoite
crystalline phase was calculated under a scanning microscope and a
transmission microscope. Furthermore, the specific dielectric
constant .di-elect cons..sub.r at 3 GHz was measured by a
perturbation method.
[0064] The results are shown in Table 2.
TABLE-US-00002 TABLE 2 Fresnoite crystal Fracture Depo- Average
Electrode toughness Specific Sam- Deposited sition grain peel value
dielectric ple crystalline amount size strength K.sub.IC constant
No. phase *1 [wt %] [.mu.m] [N/2 mm.sup.2] [Pa m.sup.1/2]
.epsilon..sub.r 1 Q, A, S, 1 2 34 1.33 6.8 C, F 2 Q, A, S, 4 3 39
1.51 6.8 C, F 3 Q, A, S, 9 3 43 1.55 6.5 C, F 4 Q, A, S, 20 4 35
1.42 7.1 C, F 5 Q, A, S, C -- -- 13 1.18 6.9 6 Q, A, C, F 25 7 29
1.24 7.2 *1: Q: Quartz, A: Alumina, S: Sanbornite, C: Celsian, F:
Fresnoite
[0065] As can be seen from Sample No. 1 to 4 and 6, the ceramic
sintered bodies with the respective crystalline phases of quartz,
alumina, and fresnoite deposited therein provided an electrode peel
strength greater than 20 N/2 mm.sup.2, a fracture toughness value
K.sub.IC greater than 1.2 Pam.sup.1/2, and a specific dielectric
constant .di-elect cons..sub.r of 10 or less.
[0066] In addition, as can be seen from a comparison among Sample
No. 1 to 4, with the increase in the TiO.sub.2 amount, the relative
deposition amount of the fresnoite crystalline phase in the
sintered body was increased to result in a fracture toughness value
K.sub.IC greater than 1.3 Pam.sup.1/2 for all of the samples. More
specifically, it has been determined that these samples are less
likely to cause the development of cracks, and thus are excellent
in terms of substrate strength. Furthermore, it has been determined
as a result that cracks are less likely to be caused or developed
at electrode joint interfaces, thereby resulting in increased shock
resistance.
[0067] On the other hand, as in the case of Sample No. 5, in the
case of no fresnoite crystalline phase produced, it has been
determined that the fracture toughness value K.sub.IC is low, and
the electrode peel strength is also low.
[0068] It is to be noted that when the ratio of TiO.sub.2 was
greater than 10 parts by weight with respect to 100 parts by weight
of the main constituent ceramic material in the low temperature
cofired ceramic material as in the case of Sample No. 6, the
deposition of the fresnoite crystalline phase was increased,
whereas the deposition amounts of the other crystalline phases such
as sanbornite and celsian was relatively decreased, thereby
resulting in a tendency to homogenize the crystal structure. In
this case, such a stress distribution that prevents the development
of cracks was decreased to result in a tendency to decrease the
fracture toughness value K.sub.IC. In addition, it is also
considered that as a result of the increased average grain size for
the fresnoite crystal phase, the crystal grain boundaries were
decreased to decrease the fracture toughness value K.sub.IC.
[0069] While preferred embodiments of the present invention have
been described above, it is to be understood that variations and
modifications will be apparent to those skilled in the art without
departing from the scope and spirit of the present invention. The
scope of the present invention, therefore, is to be determined
solely by the following claims.
* * * * *